A trial court may permit a witness who is qualified “by knowledge, skill, experience, training, or education” to testify as an expert, if it determines that “scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue.” MRE 702. However, trial courts must be vigilant to ensure that the expert’s testimony remains within proper bounds: There is always the concern that jurors will disregard their own common sense and give inordinate or dispositive weight to an expert’s testimony. See People v Peterson, 450 Mich 349, 374 (1995) (noting the potential that a jury might defer to an expert’s seemingly objective view of the evidence). For that reason, trial courts must—at every stage of the litigation—serve as the gatekeepers who ensure that the expert and his or her proposed testimony meet the threshold requirements. Gilbert v DaimlerChrysler Corp, 470 Mich. 749, 782 (2004).<>>

A trial court errs when it abandons its duty to ensure the integrity of the expert’s testimony or performs its gatekeeper function inadequately. Gilbert, 470 Mich at 780. Where the proffered testimony is not relevant or not helpful because it does not involve matters beyond the common understanding of jurors, it is inadmissible under MRE 702. People v Kowalski, 492 Mich 106, 121-122 (2012). In addition to the requirements provided under MRE 702, trial courts must ensure that an expert’s testimony complies with the general rules of admissibility. See MRE 401, MRE 402, and MRE 403. Applying all these rules, courts have developed specific limitations on expert testimony that implicate a defendant’s right to have an impartial jury find the facts. As Justice Brickley explained in the context of a criminal sexual conduct case, because of the danger that jurors might be tempted to defer to an expert on the issue of guilt, courts have established “appropriate safeguards” to accommodate the need for expert testimony in specific circumstances while avoiding the possibility that a jury might unduly rely on the expert’s testimony: Given the nature of the offense and the terrible consequences of a miscalculation—the consequences when an individual, on many occasions a family member, is falsely accused of one of society’s most heinous offenses, or, conversely, when one who commits such a crime would go unpunished and a possible reoccurrence of the act would go unprevented—appropriate safeguards are necessary. To a jury recognizing the awesome dilemma of whom to believe, an expert will often represent the only seemingly objective source, offering it a much sought-after hook on which to hang its hat. [People v Beckley, 434 Mich 691, 721-722 (1990). <>>

An expert may testify regarding the characteristics of sexually abused children, but only for the purpose of explaining potentially unusual behaviors. Peterson, 450 Mich at 365. The expert may not offer an opinion as to whether the victim was actually abused. Id. A prosecutor may not present expert testimony on the characteristics of drug dealers—commonly referred to as profile evidence—in order to establish that the defendant was in fact a drug dealer. People v Hubbard, 209 Mich App 234, 241-242 (1995). The prosecutor may, however, present such evidence as background or modus operandi evidence, but the trial court and the parties must be careful to ensure that the testimony is not offered as substantive evidence of guilt and the expert should not be permitted to opine that the defendant is guilty or otherwise testify in such a way as to imply that the defendant is guilty. People v Williams, 240 Mich App 316, 320-321; 614 NW2d 647 (2000). Although an expert’s testimony may “embrace” ultimate issues to be decided by the jury, see MRE 704, the expert may not generally offer an opinion on fault, guilt, or a witness’ truthfulness. See Kowalski, 492 Mich at 129 (stating that an expert may testify about the phenomena of false confessions and interrogation techniques, but may not comment on the truthfulness of a defendant’s confession); People v McGillen, 392 Mich 278, 285-286 (1974) (stating that a medical doctor cannot offer expert testimony that the victim was actually raped or that she is truthful); O’Dowd v Linehan, 385 Mich 491, 513 (1971) (holding that it was error to allow the expert to “fix the blame for the accident” because there was nothing exceptional about the evidence that required an expert opinion on the ultimate issue).<>>

With regard to evidence concerning gang membership and gang culture, there are no published Michigan authorities that specifically address its permissible scope. Nevertheless, other courts have held that such testimony can be helpful to jurors. See People v Memory, 182 Cal App 4th 835, 858 (2010) (stating that evidence of gang membership is admissible to prove motive); New Jersey v Torres, 183 NJ 554, 569; 874 A2d 1084 (2005) (listing cases where courts have determined that expert testimony about gangs and gang culture is relevant and helpful to the jury); United States v Mansoori, 304 F3d 635, 654 (CA 7, 2002) (holding that the police expert’s testimony on the history, structure, and involvement of the Travelling Vice Lords gang was useful to the jury); United States v Lemon, 239 F3d 968, 971 (CA 8, 2001) (“Evidence of gang membership is admissible if relevant to a disputed issue.”); United States v Hankey, 203 F3d 1160 (CA 9, 2000) (stating that a police expert could testify about the defendants’ gang affiliations and general tenets of gang culture to impeach testimony). Nevertheless, courts have recognized the high potential that such evidence will be unduly prejudicial. In United States v Garcia, 151 F3d 1243 (CA 9, 1998), the court reversed a defendant’s conviction for conspiracy because the only evidence that the prosecutor presented in support of the conspiracy was evidence that the defendant was in a gang: Recent authority in this circuit establishes that “[m]embership in a gang cannot serve as proof of intent, or of the facilitation, advice, aid, promotion, encouragement or instigation needed to establish aiding and abetting.” Mitchell v Prunty, 107 F3d 1337, 1342 (CA 9, 1997), cert denied, 522 US 913, 118 S Ct. 295; 139 L Ed 2d 227 (1997), overruled in part on other grounds, Santamaria v Horsley, 133 F3d 1242 (CA 9, 1998) (en banc). In overturning the state conviction of a gang member that rested on the theory that the defendant aided and abetted a murder by “fanning the fires of gang warfare,” the Mitchell [court] expressed concern that allowing a conviction on this basis would “smack[ ] of guilt by association.” Id. at 1342. The same concern is implicated when a conspiracy conviction is based on evidence that an individual is affiliated with a gang which has a general rivalry with other gangs, and that this rivalry sometimes escalates into violent confrontations. [Id. at 1246.] Although there may be evidence that gang members are generally looking for trouble or prepared for violence, that evidence does not itself establish that they have actually made plans to initiate it and, for that reason, it is not evidence of a criminal conspiracy. Id. Further, the court warned that allowing evidence of gang membership to serve as evidence of aiding and abetting or conspiracy would invite absurd results: “Any gang member could be held liable for any other gang member’s act at any time so long as the act was predicated on the common purpose of fighting the enemy.” Id. (internal quotations and citation omitted). Accordingly, expert testimony that a defendant is in a gang and that the gang members have a basic agreement to back one another up in fights is insufficient to establish a conspiracy to commit assault or other illegal acts. Id. at 1245-1246. Where an expert testifies about gang membership and culture, trial courts must be certain to ensure that the jury does not get the impression that gang membership alone equates to guilt. Evidence regarding the beliefs and practices of an organization may be relevant to explain a member’s conduct on a particular occasion, but only with an appropriate foundation and limitations. Memory, 182 Cal App 4th at 862. When admitted without a proper foundation and an appropriate limiting instruction, there is a danger that the jury will make an improper inference: “Membership in an organization does not lead reasonably to any inference as to the conduct of a member on a given occasion. Hence, the evidence was not relevant. It allowed, on the contrary, unreasonable inferences to be made by the trier of fact that the [defendant] was guilty of the offense on the theory of ‘guilt by association.’” [Id. at 859 (citation omitted).] See also Kennedy v Lockyer, 379 F3d 1041, 1055-1056 (CA 9, 2004) (stating that evidence of gang membership cannot be introduced to prove a substantive element of the crime, such as intent, because it amounts to guilt by association); Mansoori, 304 F3d at 654 (noting that the expert testified that membership is not a crime and that membership in the gang does not necessarily indicate that the member is involved in illegal activities and that the trial court instructed the jury that it is not illegal to be a member of, or associated with, a gang); United States v Roark, 924 F2d 1426 (CA 8, 1991) (ordering a new trial because the government’s witnesses’ testimony about the Hell’s Angels organization unfairly introduced improper propensity evidence and transformed the theme of the trial into one of guilt by association).<>>

An expert may not testify that the defendant is guilty, or offer an opinion that a disputed act actually occurred. Peterson, 450 Mich at 365; McGillen, 392 Mich at 285-286. Similarly, although evidence that a defendant is a member of a gang implicates improper propensity evidence, when the evidence is admitted for a relevant purpose and the jury is properly instructed on the limits of evidence, it may be admissible under MRE 404. People v VanderVliet, 444 Mich 52, 74-75 (1993); Memory, 182 Cal App 4th at 862. <>>